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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

he measured the proper amount refrigerant (1.65 lb) in the system. Not sure how he did that.

In this thread, we independently came up with 1.65 lb for the E39s built after 12/1997 so that's likely the correct weight.

I'm very curious HOW one would measure that though.
- We can easily measure the 34°F temperature at the vent blowing cold air (in the shade, ambient <75°F, relative humidity <60%) ...
- And we can easily measure the low-side pressure of 25 to 45 psi ...
- But how do we measure the actual WEIGHT of the R-134a refrigerant?

I appreciate your frustration. I also appreciate that you can "ballpark" freon and end up with a system that works perfectly well. However, there is only one 100% correct way and that is to take your car to someone who has the machine that can withdraw your freon and then reinstall it by WEIGHT. If a system already has *some* freon in it (let's say we don't know whether it is low, right on, or high). The way I do it is by the superheat method. You can google superheat and find the explanation for why it works and how it works. Basically, if you know the ambient temperature, the ambient humidity, and the temperature at the condenser inlet and have a superheat chart for the type freon being used, you add freon (or in a very few cases let it out) until you get to the right number of superheat degrees. Like for my home AC unit which uses R22, I like to run about 8 degrees of superheat which means I add freon until I get a reading at my condenser of 8 degrees higher than the super heat value for the temp and humidity THAT DAY. If you know what you are doing, you can get a very high performing AC system and never know the weight of freon in the system. But, to be accurate 100% of the time, you start with no freon in the system and then add the weight the manufacturer says is needed. That ideal charge will produce different system pressures in your AC system depending on outside temp and humidity. That is why you just can't add until you get a certain low pressure reading. Nor can you just add freon until you get 4 degrees centigrade at the evaporator. It don't work datta way...trust me or ask an AC guy you know.

For the record, I read EVERYTHING on bimmerfest I could find on how to refill the AC and came up with this somewhat obtuse "summary" of which fluid and how much to use for the AC (all the fluids are listed in this post).

As always, please correct or improve so that the summary is generally useful to others.

- Air conditioner: Refrigerant 134a (aka R-134a) with poly alkylene glycol oil, sometimes referred to as poly alkaline glycol oil (aka PAG refrigerant oil). Bentley book II, 640-2 & 640-3 & 640-23. The PAG oil is known by other names such as ND8, PAG46, and BMW PN: 82.11.1.468.042 and travels with the refrigerant as a mist. Best to empty and then refill refrigerant by weight; second best is the temperature method (i.e., in the shade, ambient temperature less than about 75°F and relative humidity below about 60% - then add R-134a until the evaporator exit air temperature with A/C set on max at 60°F is 4°C/39°F or colder - the best you can do without MoDIS is probably the center-dash vent at something like 10°C/50°F); third best is the pressure method (i.e., add refrigerant until the low-pressure side is 25 psi to 45 psi ... aim for around 32 psi (assuming shade, ambient, & humidity listed prior); worst is by can weight (e.g., adding a 12oz by weight can or a 16oz can by weight but the AC is a critical-charge system that won't tolerate refrigerant quantities much outside + or - .05 kg). [Volume: E39's built up to 12/97 contain 1,225 grams +/- 25 grams (2.70 lbs +/- 0.05 lbs) of R-134a; E39s built after 12/97 contain 750 grams +/- 10 grams (1.65 lb +/- 0.03lb) of R-134a. The amount of PAG oil misted in the system is said to be about 1 ounce by volume.] Replacement Interval: Lifetime charge (sometimes the system develops a leak though).

Your thoroughness and quest for accuracy Bluebee is well-known. That is why your posts have become the definitive conclusions on the subjects you address. Your summary is right-on. Far too many people just assume more freon is better and NOTHING could be further from the truth. This is for two reasons: Excess freon, to a point, is stored in the accumulator which is partly what it is for so adding *some* if you need *some* is "ok". If you add and you don't need, it will attempt to become stored in the accumulator, but that assumes the accumulator has room for more "over-charge". You not only needlessly raise your system pressures putting the compressor at risk, but your exit temperatures at your evap will actually begin to rise. If you don't know where you are on the pressure/temperature curve already based upon the freon you are using, you can start to have big problems BEYOND just messing up your compressor. Liquids turn to gases at the wrong time and more often- vice verse! Just "adding a can" because it must be good for it right (?) is the worst thing you can do. BMW systems generally don't leak like some older systems did. On older cars using R12, they were notorious for seals drying up and freon seeping out. They got "topped off" yearly which is what has become the hang-over into the modern times and better cars. In a BMW, you either need not a drop of freon or you are chasing a leak in a system that is extremely charge-sensitive and if you truly need freon, you might as well plan on leak repair or you will become a dog chasing its tail.

On this point, I could not agree with Edjack more! Our systems are extremely well made and reflect the European "green" movement. These systems are sealed well are rarely leak a drop!

I've got an e90 that is low on 134a (hooked gauge to low pressure side). My compressor seems to engage (at least rpm's dip a bit on tach when i turn on a/c). It currently blows hot air. My radiator fan, which should turn on when a/c activated does not turn on, but does when car gets hot enough to activate to cool engine. I'd like to add some 134a to the system to see if that will fix issue for the moment. I understand that I may have a leak somewhere, just want to see if this will at least tempoarily work. Do cans of 134a, w/o the super cool, etc. stuff that autozone has for most of their products, contain the PAG oil needed? Anyone have a recommendation on which product i can buy at Autozone, O"reilly's, etc. Thanks!

The Autozone generic R134a cotains a lubricating oil although I don't know if it is PAG oil. When you add your refrigerant, just remember that too much is as bad as too little. Just add a bit at a time. Use the supplied gage to determine how much to add (about 3-5 psi at a time).

+1 The stuff that Autozone sells in the taller can with the can piercer attached is fine. It's a bit pricey at like $24.99 or $29.99, but I like the type of can valve/piercer it uses. It will shut off the flow and not leak the can remainder out. If you already have the threaded adaptor, you can just buy the 12 oz. can for around $15. It has 5 ingredients and none are leak stopper iirc. It has the amount of pag oil spelled-out right on the can. Think it is called R134 plus or some such catchy name! You can trust, but as the previous poster said, don't over-fill and find your leak! This stuff has the leak-finder die in it as well. Add until compressor stops cycling (if it is). Compressor should stay on all the time you have AC selected. If/when you start getting cold air, add about another 1 minute or so max of freon flow. At the very end of adding if you get cold air, turn can fully upside down. Yes, you will be adding some liquid freon, but you will also get the PAG oil and other additives. Try to add about a 1/4 can at a time. You can actually feel how much freon is in the can by the freeze line of the can. You will feel the bottom part of the can be ice cold and somewhere toward the top of can it will become warm. That is the level of freon remaining in the can. You may see a condensation line depending on ambient humidity. You can add the whole can if you must which means your car is really low, but do it in approx. 1/4 can at a time portions and then screw the piercer back down fully. If you are at the very bottom of the green area, you are real close. BMW pressures are low compared to American cars when they are full. Don't get hung up on pressures. Just shoot for first signs of cool air and then a little more. How soon you AC quits again will tell you how fast your system is leaking. Proper BMW systems will not lose any freon over time. They do not leak "inherently". If you are at about 28# after running a bit, you are in the ballpark. DON'T try for 40# or whatever the gauge says...that's way too much! G/L

Quest Sub-Zero Synthetic A/C Booster creates a boundary of lubricant on the surface of all metal component parts of the air conditioning system, including the compressor. Quest Sub-Zero Synthetic A/C Booster increases heat transfer by guarding against lubricant migration on the heat exchange surfaces of the evaporator and condenser coil. By eliminating the energy robbing barriers caused by stagnate oil build up and carbon deposits, the system requires less energy and cools more efficiently.

Okay, I started the car and had it run about 5 mintues on max cool. I added some 134a (it was really low) and the ac/radiator fan kicked on (a good sign!). I couldn't tell if compressor was running as fan was making so much noise. Anyway, got pressure on low side up to 30#. However, with a/c on max cool, temp from vents inside car never got below outside air temp and may have even been hotter (it was about 90 degrees outside and vent temp said 103, but I was assuming that increase over ooutside temp was due to engine heat as well). I felt all the hoses and none of them felt cool, as I'm assuming at least one should feel cold. Hose from compressor to condensor did feel a bit warmer than outside air temp, but line from condensor to evaporator (is that correct, it was the other line going out of condensor) was only room temp. I felt all the lines I could reach with my hand and none of them felt cold at all.

At this point, you have very little down-side. I would check high side pressure if you can borrow and adaptor or get a manifold set. Some will disagree, but given your down-side being a trip to a specialist, I would add another can (or less if you get cool air). You can go to autozone and just get the $8.99 can of R134a only. You have pag oil and everything else you need in there in sufficient amounts. Try more freon. Worst case is that you will have some extra which will get stored in accumulator/drier. Upside is the compressor responds. Downside is the compressor hi pressure switch will shut it off to protect it. You are looking at a teardown anyway so freon will be pulled and saved.

Should this not help, then I think there is a good chance your expansion valve may be gone south. Knowing your pressures will tell us about health of compressor. I think you meant compressor bad rather than condensor.

Does your outside temp sensor work or does it read -40 degrees? Just checking--if the car "thinks" it's very cold outside the HVAC will not allow you to cool your car; this has come up here frequently.

my outside tempe sensor reads -40...it just started doing this about 2 weeks ago...this might be the cause of my AC problem..how do I fix this??

my outside tempe sensor reads -40...it just started doing this about 2 weeks ago...this might be the cause of my AC problem..how do I fix this??

+100 Man, I should know by now to ask the obvious. Obvious to me, but I guess not obvious to some. There is a game breaker right there. check wiring as well especially if you tend to run over parking barriers. Consider as many have done...relocating to a safer spot. Bmw took the sell more parts approach.

it was missing (my temp sensor)..so cheap/easy fix...and I'm totally gonna take the advice of relocating it...whos genius idea was it to put it on the bottom of the bumper of a low vehicle?? lol I cant tell you how often I DON'T pull all the way forward in parking spaces because those stupid concrete stoppers will catch my bumper...grrrrr lol

Fudman, I would say your pressures are fine. I am surprised by how much difference there was between two different days checks. 61 pounds is a tad high, but recall that a system that has not run in a long time will have a higher low side pressure as all the freon on the high side will leak back to the low side until the pressures are equal. A system that is run often and is "tight" might show 35 and 250, and the same system left unrun for a long time might check 65 and 65 low and high side respectfully. E39s have the auxilliary fan in front protected by a 50 amp fuse above the glove box. Depending on what year you have, you could have three large resistors for the three seperate speeds or the later models are controlled by the DME so they are VERY difficult to test. I tried every which way to get my fan to run off my battery charger which easily puts out 35 amps or more and it would not power it, yet the DME turned it on beautifully! The newer fans will have three wires going to them. Two good size wires Like #10 and one puny wire from the DME to control speed. You can just buy the motor. I believe Auitozone sells. Do a search. It may just be the older style fan which regulates speed through the resistors. I was not aware that the fan being dead would stop the AC from turning on. It only turns aux. fan on at idle when hot and for about 30 seconds after you shut off car when running ac.

Since your AC was running before, I would definitely let out about 10# from the low side. Do it in steps. The stuff to fill it again is dirt cheap so don't sweat a little waste. Tell your neighbor you bought some pollution credits from a steel mill =) The fan job is a PITA as it requires you to pull the front bumper. You should be able to go as low as 25# and still have enough in there to run the compressor. You could locate the low side pressure switch and jumper it out as well. Just let some out and move on! I was out of town for a while. Will be available all weekend if you need me.
Bill

P.S. whatever you do, do NOT turn the freon can upside down!!! Jeez, the mis-information here is unreal. It generally comes from the most critical people too that have no idea what they are talking about, but will never admit they may have given you bad information because they are always right and they refuse to argue with idiots. This could explain why you see them talking to themselves a lot..

Hello 540iman, I am having some AC problems myself and I have a quick question for you. If the AC system has not been run for awhile (like mine) and maybe the low and high side pressures are the same (my low side is 33PSI, don't know my High side), how do you get the high to be back to its normal (250 PSI right number?). Do you just run your AC? Or do you actually have to refill your high side till it gets to the correct PSI?

You do not add freon to the high side ever-thats#1 and the basic answer to the second part is when the compressor starts the high and low sides will take care of themselves. Depending on the type of expansion valve employed, the high and low side pressures may fully equalize meaning the high and low will be the same or you may find that the high side holds a higher pressure and the low side will stay low. If your car has been sitting for an hour or a year, the pressures will equalize to some in-between level-not 33# however.

33# is more like what you wanna see with compressor running. You don't say whether you have ever gotten your compressor to run, but if not...i'd say you are way low on freon and it would be added to the low side. You haven't given me a lot to go on here...

OK, that is starting to make some sense, as that aligns with the code I pulled. The pusher fan sits in front of the condenser. Anyone have any ideas as to what would cause the pusher fan to stop working? Fuse? Is it somehow related to my overcharging the A/C system? There is nothing on this in my Bentley. My current system (low side) pressure is now around 35 psi at around 65F-70F, so the compressor should kick on but is not.

The low side should read anywhere from 25-45psi with the AC running. The high side should read 100-150 degrees above ambient temp. Ie. 70* ambient temp high should be 170-220psi. The low side looks good, If you have a thermometer you can measure te inside temperature through the vents and it should be anywhere from 40*-55*. Anything warmer needs to be looked at. Are there any leaks in the system? The compressor clutch cuts on and off? Are there any places on the hose or compressor that look dirtier than others?

Also my auxiliary fan stopped working and I cleaned it out with some electrical cleaner and it had a ton of dirt in there. I tapped it with a non-marring hammer and hooked 12 volts to it and voila...it spins again. Maybe this will work or maybe not. There are only a few places in an AC system that you can check. Obviously there is the compressor, condensor, depending on the system(receiver drier for txv/accumulator for ccot), metering device(expansion valve for txv/orfice tube for ccot), and evaporator. The Auxiliary fan and the radiator fan is one of those most wouldn't think about, but eh. Also, if the fan shroud is broken it should be replaced because you are not getting the correct amount of air flow via Ram air effect. Hope some of this tid bit stuff helps.